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Power issue with the BS2 controller — Parallax Forums

Power issue with the BS2 controller

alphanerd132alphanerd132 Posts: 9
edited 2016-04-05 17:57 in Robotics
I figured out why my BOE board was only running .02 of an amp. Turns out that the BS2 can only send an I/O of .02 amp. So my question is what can I do to fix this? Can I modify the BS2 or could I just buy a new stamp controller. And if I should buy a new controller then what one should I get. Forgot to say, I am, if I can from any stamp controller, wanting to draw around 2 amps from the I/O on the main board.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    What is it you're trying to do? I am not clear on the nature of your issue.
  • alphanerd132alphanerd132 Posts: 9
    Chris Savage wrote: »
    What is it you're trying to do? I am not clear on the nature of your issue.
    Sorry. I updated the post. I am making a Humvee and, if I can, draw around 2 amps from the board.
  • Mike GreenMike Green Posts: 23,101
    All the I/O pins on all of the Stamp models (and pretty much all microcontrollers) have a limit of roughly 20ma into or out of the I/O pin. The interconnect wires and connections on the chip are not capable of handling much more current than that. If you look at the Nuts & Volts Stamp column #6, you'll find suggestions for using external transistors to handle larger currents. Parallax also sells relay boards that can be driven from an I/O pin and can switch much larger currents.
  • alphanerd132alphanerd132 Posts: 9
    Mike Green wrote: »
    All the I/O pins on all of the Stamp models (and pretty much all microcontrollers) have a limit of roughly 20ma into or out of the I/O pin. The interconnect wires and connections on the chip are not capable of handling much more current than that. If you look at the Nuts & Volts Stamp column #6, you'll find suggestions for using external transistors to handle larger currents. Parallax also sells relay boards that can be driven from an I/O pin and can switch much larger currents.
    Thanks for the info!! So the next question is A: why does parallax sell a relay board that needs ~85ma and there controllers can only give 20ma. B: why are controllers limited to that? And could I possibly make one that can handle more?
  • kwinnkwinn Posts: 8,697
    To fit the amount of circuitry required by a microcontroller into a small chip the individual components must be very small (microscopic) so they cannot handle high currents. The small signals the microcontroller provides need to be amplified hundreds or thousands of times or more to run motors, heaters, and other high power devices. That is the job of driver circuits designed for specific applications.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    alphanerd132 wrote: »
    Thanks for the info!! So the next question is A: why does parallax sell a relay board that needs ~85ma and there controllers can only give 20ma. B: why are controllers limited to that? And could I possibly make one that can handle more?

    The board requires ~85 mA for power, but that isn't sourced from the I/O pin. The I/O pin drives a transistor, which safely switched the higher current load of the relay coil. Likewise, a diode in the circuit protects the I/O pin from damage due to inductive kickback from the relay coil. These types of considerations would need to be made on virtually any microcontroller.
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